Gordon Brown is expected to disagree with his drugs advisors and return cannabis to its class B status, weekend press reports say.
Earlier this year Mr Brown made it known that he favoured a stricter law on cannabis, a view that was confirmed in a press briefing last week.
His view is likely to be contrary to that the Advisory Council on the Misuse of Drugs (ACMD). It has been conducting a review of the law and is expected to report this week with recommendations that the law remain as it is.
One member of the council has warned that if Mr Brown goes ahead with reclassification contrary to its advice “it would call into question the whole function and future of this group”.
Cannabis was moved down from the class B category to class C in 2004 by then Home Secretary David Blunkett, meaning weaker punishments for those found possessing or dealing the drug.
However, Mr Brown announced the review of the law shortly after becoming Prime Minister last year.
His support for a stricter law has been commended by a group of drugs and mental health experts in a letter to The Times.
They say: “The mental wellbeing of young people is paramount. Our duty as adults is to protect them from harm.
“No one suggests that all youngsters will be influenced by a change in classification, but some will be.
“The restoration of cannabis to Class B, accompanied by a serious campaign to educate the public about the links between cannabis and mental illness, will be welcomed by everyone who has the welfare of children at heart.”
The Home Office has said that the results of the review will be announced in due course.